Looking for ET with a Metal Detector

SYDNEY, Australia, March 15 (UPI)--Finding Earth-like planets with
advanced life forms could be easier than we once thought, says one
astrophysicist.

Charles Lineweaver, of the University of New South Wales, says the
probability of a solar system harboring life-sustaining planets is
directly proportional to the amount of metal in that system's star.

"The ability to produce "Earths" is zero at low metallicity and
increases linearly with metallicity of the host star," Lineweaver said.

While too little metal content in a star precludes formation of
Earth-like planets, too much will lead to massive "Jupiters,"
incompatible with life and liable to collide with planets similar to
ours. Earth-like planets only form when the right amount of metal is
present. Lineweaver terms this the "Goldilocks" planetary selection
effect.

"These are reasonable assumptions," said Guillermo Gonzalez, Professor
of Astronomy at the University of Washington, and an earth-origins
researcher. "These ideas are not original to Lineweaver, but his is the
best quantitative treatment to date," Gonzalez told United Press
International.

Stars are critical to Earth-like planetary formation, because they
create the metals the planets use as raw material, Lineweaver said.

"These heavy elements, or 'metals', were not produced in the Big Bang.
They result from fusion inside stars and have been gradually building up
over the lifetime of the universe," Lineweaver said. "The star formation
rate plays a dual role in this analysis since stars make planets and
stars make metals."

Using metal content, Lineweaver said he obtained the probability for a
solar system to harbor an Earth-like planet. Combining this probability
with current estimates of star formation rate and metal buildup in the
Universe, he worked out an estimate of how old possible Earth-like
planets could be.

"Three-quarters of the Earth-like planets in the Universe have an
average age 1.8 billion years older than the Earth," Lineweaver said.

"I think the average age he quotes is a bit large, since most other
galaxies are less massive than the Milky Way, and, hence, more
metal-poor," Gonzalez told UPI.

Lineweaver said his analysis might reveal clues about the nature of life
on other planets. "If life forms readily on Earth-like planets, this
analysis gives us a rare clue about how we compare to other life that
may inhabit the Universe," he says.

That clue indicates highly advanced aliens may not be so far-fetched.
"The average Earth in the Universe is 1.8 billion years older than ours.
And, if life exists on some of these Earths, it will have evolved, on
average, 1.8 billion years longer than we have."

"Theoretical constructs, like this one by Lineweaver, are valuable and
timely," says John Delano, distinguished teaching professor of Earth and
Atmospheric Sciences at the State University of New York. "The
implications of these ideas are profound."

So how might we find life on other planets? According to Lineweaver,
it's as simple as using metal detectors in outer space.

Gonzalez concurs, but with a simple caveat. "This sounds reasonable, but
the TPF should search a broader parameter range," Gonzalez told UPI.
"There are other factors that make a planet truly 'Earth-like.'"

Lineweaver's paper will appear in a future issue of the journal Icarus.